Why does the water in a car radiator sometimes boils explosivebly when the radiator cap is removed?

Why does the water in a car radiator sometimes boils explosivebly when the radiator cap is removed?
Water boils at 212F at Sea level pressure, 14.5 psi or so. If the pressure is increased, so is the boiling point. This is how a pressure cooker cooks with water at up to 500 degrees, and how a nuclear reactor can heat water to almost 3000 degrees, without boiling. Also, water will boil at room temperature or less, if you reduce the pressure, such as applying a vacuum pump to the container. When you open that radiator cap, it causes a drastic change in pressure, a drop. If the water is only warm, just under 200F, say, it will likely just boil violently. If it is above the normal boiling point, that pressure was all that was keeping it liquid. This violent change from liquid to gas is known as flashing. It changes states of matter, and releases a huge and violent amount of energy. This flash is what turns the turbines in power plants, by the way.